Propellant composition using carboxyterminated copolymers of butadiene and ferrocene derivatives

ABSTRACT

COPOLYMERS OF BUTADIENE AND VINYL FERROCENE (VF) ARE DISCLOSED ALONG WITH PREPARATIVE PROCEDURES THEREOF. THE COPOLYMERS ARE PRODUCED IN AN ORGANIC SOLVENT WHEN POLYMERIZATION IS INITIATED BY A CARBOXY-CONTAINING AZO COMPOUND, SUCH AS, AZOBIS(2-METHYL-4-CARBOXY BUTYRONITRILE), THEREBY FORMING A COPOLYMER OF BUTADIENE AND VINY;FERROCENE. THE COPOLYMERS ARE USEFUL IN PROPELLANT FORMULATIONS AS A BINDER WHERE HIGH BURNING RATES ARE DESIRED.

3,813,306 Patented May 28, 1974 United States Patent Office 3,813,306 PROPELLANT COMPOSITION USING CARBOXY- TERMINATED COPOLYMERS OF BUTADIENE AND FERROCENE DERIVATIVES Samuel F. Reed, In, Holland, Pa., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Original application Dec. 7, 1970, Ser. No. 95,889. Divided and this application May 30, 1972,

'Ser. No. 257,560

Int. Cl. C06d /06 Us. (:1. 149-193 V 3 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCE TO RELATED APPLICATIONS This is a division of application Ser. No. 95,889, filed Dec. 7, 1970.

BACKGROUND OF THE INVENTION Considerable literature exists on the preparation of polybutadiene with carboxy-terminal groups prepared by both anionic and free radical initiators.

The preparation of vinyl ferrocence may be accomplished by the method disclosed by F. S. Arimoto and A. C. Haven, J. Am. Chem. Soc. 77, 6925 (1955).

Well known in the propellant field is the fact that the burning rate of many solid propellants can be increased by the introduction of certain iron-containing additives. Many ferrocene derivatives have been utilized as additives for this purpose, usually in the form of liquids which also serve as plasticizing agents. In the liquid state the ferrocenes display the inherent disadvantages characteristic of liquid additives, such as loss by evaporation, migration, etc., and consequently, the propellant systems sufier, particularly on long term storage.

Thus, a need exists for a modified form of ferrocence additive which form is not subject to being lost by evaporation or migration from a stored propellant composi tion.

An object of this invention is to combine the ferrocene additive with the binder being utilized in the propellant system.

Another objectis to combine a ferrocene derivative and a binder material via a polymerization technique into a serviceable prepolymer suitable for propellant mixing and curing. I.

A specific object of this invention is to copolymerize a binder material and a catalyst material to provide a liquid copolymer which is capable of undergoing a cure reaction when used in a propellant composition to form a rubber-like binder material having a burning rate catalyst agent as an integral part thereof.

SUMMARY OF THE INVENTION Vinyl ferrocene is copolymerized wtih butadiene in an inert organic solvent after the polymerization reaction is initiated by a carboxy-containing azo compound, such as azobis(2-methyl-4-carboxy butyronitrile). The liquid copolymer is characterized by its molecular weight which is in the range of from about 1000 to about 10,000, its carboxy-end group content from about 0.5 weight percent to about 9 Weight percent, and its iron content from about 0.5 Weight percent to about 15 weight percent. The liquid copolymer is capable of undergoing a cure to a final rubber-like state.

DESCRIPTION OF THE PREFERRED EMBODIMENT The copolymer'formed by reaction of butadiene with vinyl ferrocene is useful as a combination binder and burning rate catalyst for solid propellant compositions.

The liquid copolymer is characterized by its preferred molecular weight range from about 1000 to about 10,000, its preferred carboxy-end group content from about 0.5 weight percent to about 9 weight percent, and its iron content from about 0.5 weight percent to about 15 weight percent. The liquid copolymer of butadiene-vinyl ferrocene is produced by a procedure as described by the descriptive technique set forth below as Example I. Table I below sets forth the experimental data on preparation of butadiene-VF copolymers. Table II below, sets forth the physical property data for butadiene-VF copolymers produced with the concentrations set forth in Table I.

The butadiene-VF mole ratios may vary from approximately 100:1 to about 1:1. The ratio of 1:1 yields a copolymer with an iron content of about 15 weight percent. The organic solvents wherein copolymerizations are conducted may be toluene or dioxane. Polymerization temperatures may conveniently be maintained in the range of 6080 C. Reaction times may vary over the range of 24-120 hours; however, a reaction time in the range of about 72 hours is preferred.

Copolymers having molecular weights ranging from about 1000 to about 10,000 carboxy-end group contents of from about 0.5 to about 9 weight percent of the copolymer, and an iron content from about 0.5 weight percent to about 15 weight percent of the copolymer are easily obtained by varying the reaction conditions and concentrations of reactants and initiators. Other representative carboxy-containing azo compounds such as 4,4-azobis- (4-cyanovaleric acid), 3,3'-azobis(3-cyanobutyric acid), and 2,2'-azobis-(2-cyanopropionic acid) may be employed as initiators for the polymerizations of this invention.

EXAMPLE I Procedure for polymerization of butadiene and vinyl ferrocene To a glass high-pressure reactor (aerosol tube) are introduced 30 ml. of dioxane, 1.0 g. (0.00465 mole) VF, and 3.26 g. (0.0196 mole) azobis(2-methyl-4-carboxybutyronitrile). The reactor is attached to a vacuum line and deaerated by three alternate freeze-thaw cycles. At this point 19.0 g. (0.352 moles) of butadiene are condensed into the reactor. The reactor is removed from the vacuum line and placed in an oil bath at 66-67 C. Heating is continued for a period of 72 hours. After cooling, the reactor is vented, the solvent removed by evapora tion and the copolymer reprecipitated by dissolving in ether followed by the addition of methanol. After decanting the solvents, copolymer is stripped of excess solvents on a rotatory evaporator and finally dried at 70-75 C. under reduced pressure (1 mm. Hg) for a period of 25 hours. The yield of copolymer is 11.2 g. (56%). Evaporation of the decanted solvents gave an additional 5.0 g. of the copolymer containing the low molecular weight copolymer and impurities. The liquid copolymer (methanol insolubles) is characterized by its molecular weight range meeting most requirements. Special Processing aids such as lecithin and trace amounts of additives known in TABLE I Experimental data on preparation of butadiene-VF copolymers Butadiene Weight Weight B V ratio Initiator copolymer Yield, (g./mmole) (g./mmole) B/V (mmole) (g.) percent 19. /352 1. 0/4. 67 95/5 10. 6 11. 2 s 17. 0/310 3.0/14. 0 85/15 9.8 13. 3 e6. 5 15. 0/280 5. 0/23. 0 75/25 9. 0 12. 3 s1. 5

TABLE H theart for their specific contributions to the ballistic, castrhyslcalpmperty datafor bumdleneNF copolymers 1b1l1ty, and storage properties of the propellant may b added to the propellant formulation.

Weight percent I clalm. M I 1 00111 Percent Fe" 1 A 11 t 1 oecu ar prope an compos1 lOl'l. comprislng a past1cizer Weight Fmmd Calcd- Fmnd Calcdof isodecyl pelgonate; metal additive; inorganic oxidizer 3 800 2 61 2 87 0 63 1 30 and carboxy terminated-copolymers of butadiene and 21,600 65 46 vlnyl ferrocene, said copolymers prepared by the process 2,200 2.85 4.08 5. 2 6. 5a WhlCh comprises reactlng vinyl ferrocene 1n an amount of Calculated C0211 weight percent made on the basis of two COzH groups per chain for the molecular weight values reported.

"Calculated Fe content made on the basis of the ratio oi cemenorners initially charged into the reactor.

The copolymers of this invention may be used as the binder-catalyst for a solid propellant composition. The copolymers may be used in the propellant composition in amounts from about 5 weight percent to about 30 weight percent. The remaining propellant ingredients exclusive of processing aids (such as lecithin) and trace amounts of other additives (e.g., stabilizing, ballistic, special curative, and the like) may be comprised of a plasticizer such as isodecyl pelargonate, a metal fuel such as aluminum, and an inorganic oxidizer such as ammonium perchlorate.

An example of a propellant composition using the copolymers of this invention is set forth under Example II below.

EXAMPLE II Ingredient: Weight percent Butadiene/vinyl ferrocene copolymer binder 10.0 Isodecyl pelargonate plasticizer 10.0 Aluminum powder 10.0 Ammonium perchlorate 70.0

The burning rate for the propellant formulation of Example II compared with a standard containing only butadiene, as binder, is higher by about 20 percent. The propellant formulation of Example II does not require an additional burning rate catalyst, and the formulation may be varied to incorporate a higher binder content and a higher iron content. The iron content may also be controlled by the amount of vinyl ferrocene copolymerized with butadiene as well as the amount of copolymer selected for use in the formulations. Those skilled in the art will recognize that the other propellant ingredients may be varied to include metal additives (e.g., aluminum powder or other powdered metals used in the art) in amounts from about 5 to about 20 weight percent, inorganic oxidizer such as, ammonium perchlorate from about 10 to about 72 weight percent. Other plasticizers may be used with the copolymers of this invention. Among the important plasticizers are nonvolatile organic liquids or low melting solids, especially the phthalic, adipate, and

' sebacate esters, and aryl phosphate esters. Plasticizers content is determined by the desirable properties required for a propellant formulation. Generally, plasticizer amounts from about 5 to about 30 weight percent is the about 1 mole and a suitable polymerization initiator in an inert organic solvent with a butadiene in an amount from about 1 mole to about 100 moles at a reaction temperature and for a reaction time period sufficient for said reaction to take place after which solvent removal is effected and said copolymers are dried at a suitable drying temperature while under reduced pressure; said initiator being azobis(2-methyl-4-carboxy butyronitrile); said inert organic solvent being selected from dioxane and toluene; said reaction temperature being in the range of about 60 C. to about 80 C.; raid reaction time being from about 24 hours to about 120 hours; said drying is accomplished at a suitable temperature in the range of about C. to about C. and said reduced pressure is in the range of about 1 millimeter; said copolymers being characterized by a molecular weight in the range from about 1000 to about 10,000, carboxy-end group content of about 0.5 weight percent to about 9 weight percent, and an iron content of about 0.5 weight percent to about 15 weight percent.

2. The composition of claim 1 and wherein said copolymers are present in an amount from about 5 weight percent to about 30 weight percent; said plasticizer isodecyl pelargonate is present in an amount from about 5 weight percent to about 30 Weight percent; said aluminum metal additive is aluminum powder which is present in an amount from about 5 weight percent to about 20 weight percent; and said inorganic oxidizer is ammonium perchlorate which is present in an amount from about 10 weight percent to about 70 weight percent.

3. The composition of claim 2 and wherein said copolymers are present in an amount of about 10 weight percent; said isodecyl pelargonate is present in an amount of about 10 weight percent; said aluminium powder is present in an amount of about 10 weight percent; and said ammonium perchlorate is present in an amount of about 70 weight percent.

References Cited UNITED STATES PATENTS 3,598,850 8/1971 Dewey 149-19 X 3,640,963 2/1972 Bilow 14919 X BENJAMIN R. PADGETT, Primary Examiner Us. 01. X.R. 

